Rh-Catalyzed Synthesis of Coumarin Derivatives from Phenolic Acetates and Acrylates <i>via</i> C–H Bond Activation

An efficient annulation strategy involving the reaction of phenolic acetates with acrylates in the presence of [Rh₂(OAc)₄] as catalyst and formic acid as reducing agent, leading to the high yield synthesis of coumarin derivatives, has been developed. The addition of NaOAc as a base increased the yield of the products. The reaction is quite successful for both electron-rich as well as electron-deficient phenolic acetates, affording coumarins with excellent regioselectivity, and proceeds <i>via</i> C–H bond activation proven by deuterium incorporation studies